1111, 111, 1111 - block was easy to find, but area around it was protected so not so easy to get to. With no kit the solution is to stack jump up *above* the gold block, drop down onto it, then walk backwards off it and take a screenshot as you fall. Placing water at bottom before you start is possible and avoids fall damage. This is a bit tricky, but can be much easier if you brew a potion of slow falling. Also using an elytra is obviously also an option for this one.

Underwater temple - this was simply swim in, and find the sign. The guardians are a bit nasty, but you just need to keep moving, swimming around pillars and things to break line of sight. A door was placed not too far to sign to help avoid drowning. Water breathing, night vision, and good armor would all make this easier but are not essential.

The end - this sign was placed just one block above the void in the nether. If you use bucket of water and bucket of lava you can make a cobble pillar downwards, you can dig down that to the right level and then just build a block bridge across to the gold block with the sign on (the protection field was very small). Alternative methods and dropping down from above, perhaps with slowfalling - take a screenshot and then, well, die. Or use an elytra (I thought no-one would be crazy enough to fly around 1 block above the void with their elytra - i was wrong!)

The bedrock - sign was placed in the bedrock in such a way as it was not possible to see it unless you crawled into a 1x1 gap. flow protection was disabled, so the easiest way to do this is to place a bucket of water above and swim in to read the sign. (This challenge was also under an apparently unexplored mineshaft which i thought would make it a bit more interesting)

The lava! , this was very easy - but did require bravery and accuracy. If you jumped into the lava sea at exactly the right block, you would fall through the lava onto a ladder below. With no fire protection or armor this would take you down to half a heart, but there was also golden apples in the chest which would stop things getting that bad if you were quick.

Any feedback would be much appreciated. This was a relatively short, simple (but kinda tricky) challenge, i enjoyed building it - so there might very well be another one (perhaps more sophisticated).